nodejs dynamic setting less

In front-end development, we often use Less to enhance the functionality and maintainability of CSS. However, in the process of using Less, we will inevitably encounter the need to dynamically set the Less file according to the environment. For example, in a development environment we may want to enable Less's sourceMap, but in a production environment we need to disable it. So, how to dynamically set Less in Node.js?

First, we need to install two Node.js modules:

1. less: used to compile Less files.
2. parse-duration: used to parse time strings.

The installation command is as follows:

npm install less parse-duration --save-dev

Next, we can start to dynamically set Less. The following is an example:

const fs = require('fs');
const path = require('path');
const less = require('less');
const parseDuration = require('parse-duration');

// 根据环境变量设置Less参数
const env = process.env.NODE_ENV;
const lessOptions = {
  sourceMap: env === 'development' ? { sourceMapFileInline: true } : null
};

// Less文件路径
const lessFile = path.join(__dirname, 'style.less');

// 编译Less
less.render(
  fs.readFileSync(lessFile, 'utf8'),
  Object.assign({}, lessOptions, {
    // 控制台输出信息
    log: {
      level: 4, // 编译成功时输出level: 3的信息，编译失败时输出level: 4的信息
      info(str) {
        console.log(str);
      },
      debug(str) {
        console.log(str);
      },
      warn(str) {
        console.warn(str);
      },
      error(str) {
        console.error(str);
      }
    }
  }),
  (err, output) => {
    if (err) {
      console.error('Less编译失败:', err);
      return;
    }
    console.log('Less编译成功:', output.css);
    // 如果开启了sourceMap，同时生成sourceMap文件
    if (lessOptions.sourceMap) {
      fs.writeFileSync(`${lessFile}.map`, output.map);
    }
  }
);

In the above example, we determine whether to enable sourceMap by reading environment variables, and use the Object.assign() method to pass the settings to Less. In addition, we can also find that Less compilation provides rich console output information to facilitate our debugging and troubleshooting.

It should be noted that Less will use asynchronous callbacks during compilation, so we need to put the compilation logic in the callback function. At the same time, Less provides a wealth of configuration items, such as setting the output target file, setting variable values, and so on.

In addition to compiling Less, we can also use the watch() method to monitor changes in the Less file and automatically recompile it. For example:

// 监视Less文件变化
fs.watch(
  lessFile,
  Object.assign({}, lessOptions, {
    // 禁用缓存
    cache: false,
    // 自动重新编译
    async: true,
    poll: 300, // 轮询时间，单位ms
    changed: (eventType, changedFile) => {
      console.log(`${eventType} "${changedFile}", 重新编译Less`);
      // 重新编译
      less.render(
        fs.readFileSync(lessFile, 'utf8'),
        Object.assign({}, lessOptions, {
          filename: lessFile // 指定文件名
        }),
        (err, output) => {
          if (err) {
            console.error('Less编译失败:', err);
            return;
          }
          console.log('Less编译成功:', output.css);
          // 如果开启了sourceMap，同时生成sourceMap文件
          if (lessOptions.sourceMap) {
            fs.writeFileSync(`${lessFile}.map`, output.map);
          }
        }
      );
    }
  })
);

In the above example, we used the fs.watch() method to monitor file changes. For each change, we recompile Less, output information to the console and generate sourceMap files.

In actual projects, we may encounter more complex Less configuration requirements. However, through the above examples, we can master the basic method of dynamically setting Less, and can expand and modify it as needed. Therefore, dynamically setting Less is an important skill in Node.js development and is worthy of our in-depth study and application.

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